Hacker News Reader

Comment by PatentTroll | Hacker News Reader

I think you just invented the dirigible?

Ha, yes.

I guess another way to phrase the question would be: why don't they use dirigibles to solve extended air time problems?

Dirigibles require huge volumes, because the lifting power of gas is small. Those huge volumes make for a relatively weak, slow, and difficult-to-maneuver craft. A big reason why airships disappeared in favor of airplanes was that airships had a really tough time handling or avoiding bad weather because of these limitations.

I have a blurry recollection of seeing an aircraft design that was a combination of an airplane and a dirigible. It looked like a poofy manta ray, an inflated rigid lifting body or flying wing. It wasn't quite VTOL & needed a very short runway, but it also gained more maneuverability in flight. Maybe it was too much of a compromise though.

Could it be this one [0], or its predecessor [1]?

[0] http://www.latimes.com/business/la-fi-lockheed-martin-aircra... [1] https://en.wikipedia.org/wiki/Lockheed_Martin_P-791

Perhaps you're thinking of the infamous 'Deltoid Pumpkinseed'[1][2] ?

[1] https://en.wikipedia.org/wiki/AEREON_26

[2] https://www.amazon.com/Deltoid-Pumpkin-Seed-John-McPhee/dp/0...

You mean this one?

http://mashable.com/2017/05/24/airlander-butt-plane-successf...

There's actually been more than one of these types of aircraft (known as Lighter Than Air - or LTA Aircraft), either as an idea or prototype throughout history.

That type of vehicle is called a hybrid airship!

[1] https://en.wikipedia.org/wiki/Hybrid_airship

The lifting power of helium is small, as opposed to hydrogen. Also, helium has supply problems.

Is it not possible to have a modern airship with hydrogen as its primary lifting agent?

Hydrogen doesn't buy you that much additional lifting power.

Air is about 1.2kg/m^3 at STP, so that's the theoretical maximum you can lift with a cubic meter of gas bag. (And you can only get that value if you could somehow hold a vacuum, of course.)

Hydrogen is about 0.09kg/m^3 at STP, so you can lift about 1.1kg/m^3. Helium is about 0.18kg/m^3, so you can lift about 1kg/m^3. Helium is twice as dense, but that only costs you about 10% of your lifting power since both are so light compared to air.

I see no reason you couldn't use hydrogen, but I don't know if anyone would want to take the risk. (Specific flaws of the Hindenburg aside, hydrogen is explosive across a distressingly wide range of mixture ratios with air.) If you did use hydrogen, I think the main motivation would be avoiding the use of scarce helium, not the minor increase in lift capacity.

If it's an unmanned drone-blimp, the safety issue because somewhat less critical.

But still critical enough to make it impractical. How would you do maintenance on a hydrogen airship without risking the people doing the maintenance? And you'd never be able to fly over populated areas.

It is possible but we all know what happened to the Hindenburg. Using hydrogen is asking for a fire to happen.

https://en.m.wikipedia.org/wiki/Hindenburg_disaster

Keep in mind that the Hindenburg was supposed to be helium filled, but due to import restrictions they couldn't get enough.

Far more helium airships have wrecked than hydrogen airships, even counting only before the Hindenburg.

Wrecked, yes, but they probably didn't burn like a torch with people jumping out of them to avoid burning alive.

What you saw was the engine-fuel burning on the ground; the hydrogen went straight up in flames and burnt no-one.

Vacuum still has the best lifting power of them all..

We just need a material as light as a balloon but rigid enough to hold its shape and maintain a huge vacuum at 1 atmosphere outside pressure.

Perhaps graphene aerogel, with a nonpermeable graphene casing?

I'm not sure of what its behavior would be with all its air sucked out, though.

like a hair full of nothing..

I assume huge volumes are also easily detectible?

Seems reasonable. All else being equal, your radar cross section is proportional to your actual cross section. Plus it's probably easy to spot a blimp with your eyes.

The U.S. military is way ahead of you, they've been used for extended surveillance in war zones since 2004: http://www.nytimes.com/2012/05/13/world/asia/in-afghanistan-... and even domestically: https://theintercept.com/2017/04/24/nsa-blimp-spied-in-the-u...

And before that, I believe surveillance blimps have been used in some form or another since the 19th century.

Not to mention outside Washington DC. :)

https://www.washingtonpost.com/news/the-switch/wp/2015/10/28...

Jesus, they shaped it like a giant bomb. No wonder everyone is uncomfortable. :-/

They are used to solve extended air time. That's what a weather balloon is.

If what's bugging you is why lighter-than-air vehicles aren't used for commercial transportation, that's an entirely different issue.

weather balloons are typically not up for that long, 90 or so minutes on average. So I don't think that's solving the extended air time. In fact they are pretty much designed to go up and pop and come back down. Lighter than air in general can be used to solve extended air time, and we're back to dirigibles, not weather balloons.

The Stanford Student Space Initiative's valbal is an interesting project where they add a lightweight set of ballast and a valve to a weather balloon so it can maintain an altitude. They're limited by power, the amount of ballast, and how much gas they can bleed but they can get flight times of days. https://stanfordssi.org/blog/ssi-52-breaks-world-record-agai...

Well, I'm disappointed that the majority of their flights are this short. I thought there were some of them which were permanent atmospheric weather stations.

But short flight times don't really have to be the case, because it seems that they can fly for extended periods of time: one of NASA's balloons stayed up for 46 days [0]. The US air force also uses balloons as surveillance stations, though I don't know the actual flight time of these [1][2]. JLENS was supposed to stay up for 30 days at a time.

[0]: https://www.nasa.gov/centers/wallops/news/supertiger-record....

[1]: https://en.wikipedia.org/wiki/Tethered_Aerostat_Radar_System

[2]: https://en.wikipedia.org/wiki/JLENS

sure but these aren't really weather balloons. the last two are basically tethered dirigibles. the first one is the closest and it's more like what project loon is doing. Yes, it's true, balloons can stay up for long periods of time, but this is not how weather balloons are made or what they are designed for. Weather balloons are designed to pop at a specific pressure and fall. As the balloon rises, the volume of gas expands due to there being less atmospheric pressure. At a point the balloon pops and it falls back to earth. The loon and the balloon in your first link probably use a system that adjusts the pressure in the balloon by compressing it into a storage container. This allows it to "hold" an altitude and keep the balloon from ascending until it bursts. Also, at least in loon's case, it uses a different material than a standard weather balloon. This probably also plays a roll in it's expandability, resistance to long term UV and keeping itself from popping.

Project Loon seems to be doing fine. They're using balloons to keep equipment aloft for months at a time.

sure, but I wouldn't exactly call that a weather balloon.

That does bug me actually. I want a Jules Verne-esque air-cruise-ship tour round the world.

Jules Verne was an advocate of heavier-than-air flying machines though.

Ok well leave out the man himself and include instead the brass-covered super-geared world he created.

I want a steampunk blimp ok? There. You made me say it.

You want Castle Wulfenbach.

https://www.google.co.uk/amp/s/girlgeniusadventures.com/2013...

Helium is rare and expensive and becoming even more so as time goes on.

Hydrogen has this nasty habit of being extremely flammable.

Rigid or semi-rigid airships when scaled up are really difficult to moor and arrange ground handling for, which is why some of the recent prototypes that have been flown integrate skirts and reverse-hovercraft like suction apparatus that can hold them down on a flat field.

The empire state building was originally intended as a Zeppelin mooring location, but the plan was abandoned due to wind and inability to control a zeppelin to that level of precision.

Not sure what the flight-time is, but this is pretty cool (helium-filled RC craft that looks like an airliner and flies indoors):

https://www.youtube.com/watch?v=2Kk5EGpYuck

I wondered why this wasn't applied to suitcases to make them lighter and then common sense kicked in regarding just how much actual helium would be required to lift even an empty suitcase...

It's not even an issue of how much helium is needed; no amount of helium will make a typical suitcase buoyant.

Filling it with helium at ambient pressure wouldn't produce nearly enough lift, and increasing the pressure would make it heavier, not lighter. What's needed is not mass, but volume.

I feel like you're being deliberately obtuse. I think jianshen meant how big of a helium balloon you'd need, not how much helium you'd have to put inside the suit case.

Making them a vacuum would help better.

The article said that the lighter than air aircraft got blown around by the wind too much. They needed a drone that could loiter over a specific area for an extended period of time, presumably acting as a communication relay for disaster or war zones.

probably because the need is real, just not the "for natural disaster" reason they gave.

I assume you're only asking what address to send the summons to, huh?

Reply on news.ycombinator.com